1. Field of the Invention
This invention relates to seals for use with rotating and/or reciprocating shafts, and more particularly for use with such rotating and/or reciprocating shafts in the mixing or pumping of highly viscous materials. In another aspect, the invention relates to a process for achieving a seal around a reciprocating and/or rotating shaft. In still another aspect, the invention relates to an improvement in apparatus for working or manipulating a fluid, particularly a highly viscous fluid, at least in part by the rotary and/or reciprocal motion of a shaft.
2. Brief Description of the Prior Art
Various seals have been developed in the past to allow adequate mechanical clearances and freedom of movement of reciprocating and/or rotating shafts in operation without at the same time creating avenues for excessive leakage of the materials being worked or manipulated and for contamination, some leakage however being inherent in any seal providing such clearances.
One variety of seal which has been developed is a tortuous-path type seal known as a labyrinth seal or labyrinth packing. The principal object of this type of seal is to lengthen the flow path of materials leaking from a pump or vessel along an operating shaft associated therewith, while still providing a channel for such flow whose height roughly corresponds to the total minimum required operating clearance between the shaft and its bore.
Generally speaking, these labyrinth seals comprise a series of flanges not in contact with one another alternately projecting from a shaft and the housing for the shaft and forming a single continuous labyrinthine gap. In addition to such other disadvantages as will be made apparent, these flanges, the shaft or portion of shaft carrying these flanges, and the portion of the housing so affected generally require sophisticated machining and/or materials which effectively restrict the range of applications in which these seals may be used.
Other devices have been developed also which distort or constrict the single continuous channel formed between a shaft and its stationary housing and corresponding to a certain mechanical clearance therebetween, see, e.g., Nakamura U.S. Pat. No. 4,155,558 and commonly-assigned Hay II et al. U.S. Pat. No. 4,575,100, the latter being hereby incorporated herein by reference. Each of these other devices of which Applicant is aware, however, possesses some disadvantage in terms of initial cost, complexity, frequency of maintenance or replacement, and/or effectiveness in providing a seal to contaminants or to the materials being worked or manipulated, particularly in high pressure differential applications.
It would be desirable if there were available a more effective seal for diminishing the leakage of plastified thermoplastic polymers and the ingress of contaminants, for example, along a reciprocating and/or rotating shaft, while providing the total required minimum clearance for the rotation and/or reciprocation of the shaft in normal operation.
It would also be desirable if such a seal were one which could be easily manufactured, maintained and/or replaced, and if such a seal were not susceptible to significant wear by frictional contact between elements of the seal, between the seal and housing or between the seal and shaft.